1. Field of the Invention
This invention relates to print quality measuring methods and print quality measuring apparatus.
2. Description of the Related Art
In order to perform proper printing with a printing machine, it is necessary to control ink feeding rates properly. For controlling the ink feeding rates, it has been conventional practice to measure densities of control strips with a densitometer and determine from density data whether the ink feeding rates are proper or not. However, the density data from the control strips alone is not necessarily sufficient for attaining a proper color tone and the like for a picture area.
For this reason, a print quality measuring apparatus is used which provides control data for controlling the ink feeding rates of a printing machine. The control data is produced by comparing an image on reference paper and an image on an actual print.
The reference paper is also called proof paper, and serves as a reference indicating a color tone of finished prints to obtain proper prints. Printing paper actually printed is also called sampling paper which is extracted by the operator from a discharge station of a printing machine at certain intervals during a printing operation. The printing is considered proper when the color tone on the sampling paper substantially coincides with the color tone on the reference paper.
Where a print quality measuring apparatus is used for comparing an image on the reference paper and image on the actual print to produce control data for controlling the ink feeding rates of a printing machine, it is difficult to attain an agreement in color tone and the like in all areas between the image on the reference paper and image on the actual print. For this reason, only certain areas of these images are compared. Such areas selected for comparison do not always assure a proper color tone and the like for areas characterizing the picture.